Conventionally, there has been used an estimation method of a rotational phase angle utilizing an induced voltage in a high-speed range in a rotational phase angle sensorless controller of a permanent magnet synchronous motor (PMSM) and a synchronous reluctance motor (SynRM). However, in the SynRM and the PMSM having small magnetic flux, even in the high-speed range, the induced voltage is small under a state of low load, so that there has been a problem that estimation accuracy of the rotational phase angle deteriorates.